Voltage compensation device

ABSTRACT

A voltage compensation device according to an embodiment includes a controller including first and second coordinate transformation circuits, and first and second arithmetic parts. The first coordinate transformation circuit generates first and second outputs that are mutually-orthogonal by performing a rotating coordinate transformation of the normal-phase components of a three phase AC. The first arithmetic part calculates a system voltage based on a DC component of the first output and generates a first compensation amount corresponding to a compensation voltage set to compensate a shift of the system voltage from a preset target voltage. The second coordinate transformation circuit generates third and fourth outputs that are mutually-orthogonal by performing a rotating coordinate transformation of reverse-phase components of the three-phase AC. The second arithmetic part generates second compensation amount of a reverse-phase component of the system voltage based on DC components of the third and fourth outputs.

TECHNICAL FIELD

An embodiment of the invention relates to a voltage compensation device.

BACKGROUND ART

In a power system, there are cases where the receiving voltage at theend of the power system decreases due to a voltage drop due to theincrease of the power line impedance according to the distance from thepower substation. It is necessary to be able to utilize a constantvoltage in the power system regardless of the distance from the powersubstation.

PRIOR ART DOCUMENT Non Patent Document

[Non Patent Document 1] Y. Sasaki, T. Yoshida, N. Seki, T. Watanabe andY. Saito, “High Speed TVR for Power Distribution Lines and its TestResults”, IEEJ Transactions on Power and Energy, vol. 123.

SUMMARY OF INVENTION Problem to be Solved by the Invention

An embodiment provides a voltage compensation device that quickly andcontinuously compensates the voltage of a power system to have anappropriate value.

Means for Solving the Problem

A voltage compensation device according to an embodiment includes apower converter including an inverter circuit including a switchingelement that is of a self arc-extinguishing type, series transformersincluding primary windings connected in series to phases of athree-phase alternating current and secondary windings connected to anoutput of the power converter, and a controller generating a drivesignal driving the switching element based on voltages of the phases ofthe three-phase alternating current and supplying the drive signal tothe power converter. The controller includes a first coordinatetransformation circuit generating a first output that is a vectorcomponent of a same phase as normal-phase components of the three-phasealternating current by performing a rotating coordinate transformationof the normal-phase components and a second output that is a vectorcomponent orthogonal to the first output, a first arithmetic partcalculating a system voltage indicating a voltage value of thethree-phase alternating current based on a direct current component ofthe first output and generating a first compensation amountcorresponding to a compensation voltage set to compensate a shift of thesystem voltage from a preset target voltage, a second coordinatetransformation circuit generating a third output and a fourth outputthat are mutually-orthogonal by performing a rotating coordinatetransformation of reverse-phase components of the three-phasealternating current, and a second arithmetic part generating a secondcompensation amount that is a compensation amount of a reverse-phasecomponent of the system voltage based on a direct current component ofthe third output and a direct current component of the fourth output.The controller generates the drive signal based on the firstcompensation amount and the second compensation amount. The firstarithmetic part generates the first compensation amount to cause thecompensation voltage when the system voltage is within a prescribedrange to be less than the compensation voltage when the system voltageis outside the prescribed range.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described with reference to thedrawings.

FIG. 1 is a block diagram illustrating a voltage compensation deviceaccording to a first embodiment.

FIG. 2 is a block diagram illustrating a controller which is a portionof the voltage compensation device of the first embodiment.

FIG. 3A is a block diagram illustrating a portion of the voltagecompensation device of the first embodiment. FIG. 3B is a graph showinga setting example of a setter.

FIG. 4 is a block diagram illustrating a voltage compensation device ofa comparative example.

FIG. 5 is a block diagram illustrating a voltage compensation device ofa modification of the first embodiment.

FIG. 6 is a block diagram illustrating a portion of a voltagecompensation device of a second embodiment.

FIG. 7 is a block diagram illustrating a portion of a voltagecompensation device of a third embodiment.

FIG. 8A and FIG. 8B are conceptual views for describing the operationsof the voltage compensation device of the third embodiment.

MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings.

It is noted that the drawings are schematic or conceptual, and therelationship between the thickness and the width of each portion, theratio of the sizes between the portions, and the like are notnecessarily the same as the actual ones. Also, even in the case ofrepresenting the same part, the dimensions and ratios of the parts maybe represented differently.

The identical portions in the drawings are given the same referencesigns, and the detailed explanations thereof will be omitted. Differentportions will be mainly described.

First Embodiment

FIG. 1 is a block diagram illustrating a voltage compensation deviceaccording to the embodiment.

FIG. 2 is a block diagram illustrating a controller which is a portionof the voltage compensation device of the embodiment.

The configuration of the voltage compensation device 1 of the embodimentwill now be described.

As shown in FIG. 1, the voltage compensation device 1 of the embodimentincludes a voltage compensator 10 and a controller 80. The voltagecompensator 10 includes series transformers 11, 13, and 15, a firstpower converter 20, a second power converter 30, parallel transformers41 and 42, inductors 51 and 52, current detectors 61 and 62, alternatingcurrent voltage detectors 71 and 72, and a direct current voltagedetector 75. The voltage compensation device 1 is connected in series tothe power system by the voltage compensator 10. The power system is apower distribution system of three-phase alternating current made of aU-phase, a V-phase, and a W-phase. Hereinbelow, when viewed from thevoltage compensation device 1 connected in series to the power system,the power substation side is called upstream, and the consumer side iscalled downstream. The voltage compensation device 1 is connected to theU-phase upstream 6 a at an input terminal 2 a and is connected to theU-phase downstream 7 a at an output terminal 3 a (a u-phase). Thevoltage compensation device 1 is connected to the V-phase upstream 6 bat an input terminal 2 b and is connected to the V-phase downstream 7 bat an output terminal 3 b (a v-phase). The voltage compensation device 1is connected to the W-phase upstream 6 c at an input terminal 2 c and isconnected to the W-phase downstream 7 c at an output terminal 3 c (aw-phase). The voltage compensation device 1 detects an increase or adecrease of the voltages upstream 6 a to 6 c and downstream 7 a to 7 cof the power system and compensates the voltage of the power system tobe within the range of a target value.

The series transformers 11, 13, and 15 respectively include primarywindings 11 p, 13 p, and 15 p and secondary windings 11 s, 13 s, and 15s. The primary winding 11 p of the series transformer 11 is connectedbetween the input terminal 2 a and the output terminal 3 a and isconnected in series to the U-phase of the power system. The primarywinding 13 p of the series transformer 13 is connected between the inputterminal 2 b and the output terminal 3 b and is connected in series tothe V-phase of the power system. The primary winding 15 p of the seriestransformer 15 is connected between the input terminal 2 c and theoutput terminal 3 c and is connected in series to the W-phase of thepower system. That is, the primary windings 11 p, 13 p, and 15 p of thethree series transformers 11, 13, and 15 are connected in series to thephases of the power system.

The secondary windings 11 s, 13 s, and 15 s of the series transformers11, 13, and 15 are connected to each other at one-terminals 12 a, 14 a,and 16 a, and other-terminals 12 b, 14 b, and 16 b of the secondarywindings 11 s, 13 s, and 15 s are connected to alternating currentoutput terminals 22 a, 22 b, and 22 c of the first power converter 20.That is, the secondary windings 11 s, 13 s, and 15 s of the seriestransformers 11, 13, and 15 have a star connection and are connected tothe output of the first power converter 20.

The first power converter 20 is connected between a high-voltage directcurrent input terminal 21 a and a low-voltage direct current inputterminal 21 b. A direct current voltage is supplied to the high-voltagedirect current input terminal 21 a and the low-voltage direct currentinput terminal 21 b via a capacitor for a direct current link 24. Thefirst power converter 20 includes the alternating current outputterminals 22 a, 22 b, and 22 c outputting three-phase alternatingcurrent voltages. The alternating current output terminals 22 a, 22 b,and 22 c are connected to the secondary windings 11 s, 13 s, and 15 s ofthe series transformers 11, 13, and 15 via a filter 26. The first powerconverter 20 is an inverter device converting the direct current voltageapplied between the high-voltage direct current input terminal 21 a andthe low-voltage direct current input terminal 21 b into three-phasealternating current voltages. For example, the first power converter 20includes six switching elements 23 a to 23 f. The switching elements 23a to 23 f are self arc-extinguishing type switching elements and are,for example, MOSFETs (Metal-Oxide-Semiconductor Field-EffectTransistors), IGBTs (Insulated Gate Bipolar Transistors), etc. Theswitching elements are connected in series as high-side switches andlow-side switches. Three arms of series connections are connected inparallel to configure an inverter circuit. The inverter circuit of thefirst power converter 20 is not limited to this circuit configuration aslong as the direct current voltage can be converted into alternatingcurrent voltages having a frequency higher than the frequency of thepower system. The inverter circuit may be, for example, a multi-levelinverter circuit, a modification of a multi-level inverter circuit, etc.

The filter 26 is connected between the first power converter 20 and thesecondary windings 11 s, 13 s, and 15 s of the series transformers 11,13, and 15. In the example, the filter 26 includes inductors Lu, Lv, andLw that are connected in series to the phases and capacitors Ca, Cb, andCc that are connected between the lines. The filter 26 is a low-passfilter that converts, into the frequency of the power system, thehigh-frequency switching waveform of about several kHz to several 100kHz output by the first power converter 20. The filter 26 can include acircuit appropriate according to the frequency, the modulationtechnique, etc., of the output of the first power converter 20.

The direct current link 24 includes a capacitor supplying direct currentpower to the first power converter 20. The direct current link 24supplies, to the first power converter 20, active power supplied fromthe second power converter 30. The direct current link 24 can exchangereactive current with the power system side via the second powerconverter 30.

The second power converter 30 includes a high-voltage direct currentterminal 31 a and a low-voltage direct current terminal 31 b. Thehigh-voltage direct current terminal 31 a and the low-voltage directcurrent terminal 31 b are connected to the direct current link 24. Thesecond power converter 30 includes alternating current terminals 32 a,32 b, and 32 c. One end of the inductor 51 is connected to one of thealternating current terminals 32 a, 32 b, or 32 c, and in the example,to the alternating current terminal 32 a. One end of the inductor 52 isconnected to another one of the alternating current terminal 32 b or 32c, and in the example, to the alternating current terminal 32 c. Thatis, the second power converter 30 supplies active power to the directcurrent link 24 by operating as a converter device, and morespecifically an active smoothing filter, that converts the alternatingcurrent power input to the alternating current terminals 32 a, 32 b, and32 c into direct current and supplies the direct current to the directcurrent link 24. The second power converter 30 may be an invertercircuit having the same circuit configuration as the first powerconverter 20. Similarly to the first power converter 20, the secondpower converter 30 includes six self arc-extinguishing type switchingelements 33 a to 33 f. The switching elements 33 a to 33 f are connectedin series as high-side switches and low-side switches. Three arms ofseries connections are connected in parallel to configure an invertercircuit. As long as the inverter circuit of the second power converter30 can mutually convert between a direct current voltage and analternating current voltage of a frequency higher than the frequency ofthe electric power system, the configuration is not limited to thisconfiguration. Although the configuration of the inverter circuit of thesecond power converter 30 is the same as the configuration of theinverter circuit of the first power converter 20 in the example, adifferent configuration may be used.

A primary winding 41 p of the parallel transformer 41 is connectedbetween the lines on the downstream 7 a and 7 b side of the U-phase andthe V-phase. A primary winding 42 p of the parallel transformer 42 isconnected between the lines on the downstream 7 b and 7 c side of theV-phase and the W-phase. One of a secondary winding 41 s of the paralleltransformer 41 is connected to the other end of the inductor 51, and theother of the secondary winding 41 s is connected to the alternatingcurrent terminal 32 b of the second power converter 30. A secondarywinding 42 s of the parallel transformer 42 is connected to the otherend of the inductor 52, and the other of the secondary winding 42 s isconnected to the alternating current terminal 32 b of the second powerconverter 30. That is, the secondary windings 41 s and 42 s of theparallel transformers 41 and 42 have a V-connection to the alternatingcurrent terminals 32 a to 32 c of the second power converter 30 via theinductors 51 and 52.

The current detector 61 is connected in series between the alternatingcurrent terminal 32 a of the second power converter 30 and the secondarywinding 41 s of the parallel transformer 41. The current detector 62 isconnected in series between the alternating current terminal 32 c of thesecond power converter 30 and the secondary winding 42 s of the paralleltransformer 42. That is, the current detectors 61 and 62 detect thealternating currents flowing in the inductors 51 and 52 and outputcurrent data IL1 and IL2.

The alternating current voltage detectors 71 and 72 are connected to theupstream 6 a to 6 c side of the power system. The alternating currentvoltage detector 71 is connected between the lines of the U-phase andthe V-phase and detects the line voltage between UV. The alternatingcurrent voltage detector 72 is connected between the lines of theV-phase and the W-phase and detects the line voltage between VW. Forexample, the alternating current voltage detectors 71 and 72 includeinstrument transformers and transducers converting the outputs of theinstrument transformers into appropriate voltage levels. The alternatingcurrent voltage detectors 71 and 72 detect the voltages across theprimary windings 11 p, 13 p, and 15 p of the series transformers 11, 13,and 15, perform step-down using the instrument transformers, use thetransducers to convert the voltages into alternating current voltagedata VAC1 and VAC2 which are signals inputtable to the controller 80,and output the alternating current voltage data VAC1 and VAC2.

The direct current voltage detector 75 detects the direct currentvoltage across the direct current link 24 and outputs direct currentvoltage data VDC.

In the voltage compensation device 1 of the embodiment, the second powerconverter 30 may have another configuration as long as the directcurrent voltage and the active power can be supplied to the first powerconverter 20.

As shown in FIG. 2, the controller 80 includes a first control circuit81 and a second control circuit 82. The first control circuit 81supplies, to the first power converter 20, a gate drive signal Vg1 forcontrolling the operation of the first power converter 20. The secondcontrol circuit 82 supplies, to the second power converter 30, a gatedrive signal Vg2 for controlling the operation of the second powerconverter 30.

The first control circuit 81 includes a three-phase voltage detectioncircuit 91, abc-dq transformation circuits 92 and 102, low-pass filters93, 94, 103, and 104, a compensation voltage arithmetic part 95, dq-abctransformation circuits 97 and 107, a gate drive signal generationcircuit 111, and a PLL 112.

The first control circuit 81 receives the input of the alternatingcurrent voltage data VAC1 and VAC2, generates a compensation amountcorresponding to a compensation voltage for each phase voltage, andgenerates the gate drive signal Vg1 based on the generated compensationamounts. The first control circuit 81 divides the voltages of the phasesof the power system into the normal-phase components and thereverse-phase components and performs rotating coordinatetransformations. The first control circuit 81 generates a compensationamount according to a preset compensation voltage characteristic for thenormal-phase components of the phase voltages. The first control circuit81 generates a compensation amount by calculating the differences from atarget value for the reverse-phase components.

In the voltage compensation device 1 of the embodiment, the firstcontrol circuit 81 divides the phase voltages of the power system intothe normal-phase components and the reverse-phase components andperforms independent processing for the normal-phase components and thereverse-phase components. Hereinbelow, the normal-phase components alsoare called the normal-phase voltages, and the reverse-phase componentsalso are called the reverse-phase voltages. There are cases where theelement or element group that performs the processing of thenormal-phase voltages is called the signal processing system of thenormal-phase voltage side, and the element or element group thatperforms the processing of the reverse-phase voltages is called thesignal processing system of the reverse-phase voltage side.

The compensation voltage arithmetic part (the first arithmetic part) 95is provided in the signal processing system of the normal-phase voltageside. A compensation voltage that corresponds to the normal-phasecomponents of the system voltage is set in the compensation voltagearithmetic part 95.

The compensation voltage arithmetic part 95 sets the compensationvoltage corresponding to the normal-phase components of the systemvoltage and outputs a compensation amount corresponding to thecompensation voltage that is set.

In the compensation voltage arithmetic part 95 as elaborated below, themagnitude of the compensation voltage with respect to the magnitude ofthe normal-phase voltage is set to different relationships according tothe range of the magnitude of the normal-phase voltage.

For example, when the difference between the magnitude of thenormal-phase voltage and the magnitude of the target voltage is within aprescribed range, the magnitude of the output compensation voltage isset to 0 or an extremely small value. When the difference between themagnitude of the normal-phase voltage and the magnitude of the targetvoltage is greater than the prescribed range, the compensation voltageis set to compensate the normal-phase voltage, and the absolute value ofthe magnitude of the compensation voltage is set to increase as themagnitude of the normal-phase voltage increases. When the differencebetween the magnitude of the normal-phase voltage and the magnitude ofthe target voltage is less than the prescribed range, the compensationvoltage is set to compensate the normal-phase voltage, and the absolutevalue of the magnitude of the compensation voltage is set to increase asthe magnitude of the normal-phase voltage decreases. The prescribedrange described above is set to a range that is narrower than the rangefor the target voltage of the magnitude of the compensation voltage tobe output by the voltage compensation device 1.

On the other hand, in the signal processing system of the reverse-phasevoltage side, a compensation amount that is generated according to thedifference between the magnitude of the target voltage and the magnitudeof the reverse-phase component of the system voltage is determined.

In the embodiment, when the difference between the magnitude of thenormal-phase voltage and the magnitude of the target voltage is withinthe prescribed range, the first control circuit 81 generates the gatedrive signal Vg1 to give priority to the compensation voltagecorresponding to the reverse-phase voltage over the compensation voltagecorresponding to the normal-phase voltage. When the difference betweenthe magnitude of the normal-phase voltage and the magnitude of thetarget voltage is greater or less than the prescribed range, the gatedrive signal Vg1 is generated to give priority to the compensationvoltage corresponding to the normal-phase voltage over the compensationvoltage of the reverse-phase voltage. In the embodiment, thecompensation amount is generated by giving priority to one of thenormal-phase component or the reverse-phase component according to themagnitude of the normal-phase component of the system voltage.

The three-phase voltage detection circuit 91 receives the input of thealternating current voltage data VAC1 and VAC2, converts the alternatingcurrent voltage data VAC1 and VAC2 into the phase voltages of thethree-phase alternating current, and outputs the phase voltages. Theoutput of the three-phase voltage detection circuit 91 is supplied tothe abc-dq transformation circuits 92 and 102.

The abc-dq transformation circuits 92 and 102 receive the input of thethree phase voltages of the three-phase alternating current and performrotating coordinate transformations, e.g., dq transformations. The dqtransformations perform dq transformations of the phase voltages byusing Formula (1). ω of Formula (1) is the angular frequency of thethree-phase alternating current and is, for example, 2π×50 [rad/s] or2π×60 [rad/s].

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack & \; \\{\begin{bmatrix}d \\q\end{bmatrix} = {{\frac{2}{3}\begin{bmatrix}{\sin\;\omega\; t} & {\sin\left( {{\omega\; t} - {\frac{2}{3}\pi}} \right)} & {\sin\left( {{\omega\; t} + {\frac{2}{3}\pi}} \right)} \\{\cos\;\omega\; t} & {\cos\left( {{\omega\; t} - {\frac{2}{3}\pi}} \right)} & {\cos\left( {{\omega\; t} + {\frac{2}{3}\pi}} \right)}\end{bmatrix}}\begin{bmatrix}a \\b \\c\end{bmatrix}}} & (1)\end{matrix}$

The abc-dq transformation circuit (the first coordinate transformationcircuit) 92 of the signal processing system of the normal-phase voltageside performs a dq transformation of the normal-phase components of thephase voltages. In the example, the dq transformation is performed byinputting the phase voltages of the R-phase, the S-phase, and theT-phase respectively as (a, b, c) of Formula (1).

The abc-dq transformation circuit (the second coordinate transformationcircuit) 102 of the signal processing system of the reverse-phasevoltage side performs a dq transformation of the reverse-phasecomponents of the phase voltages. In the example, the dq transformationis performed by inputting the phase voltages of the R-phase, theT-phase, and the S-phase respectively as (a, b, c) of Formula (1). Thenormal-phase components and the reverse-phase components of the systemvoltage are divided by such a connection. The normal-phase voltages thatare divided are input to the abc-dq transformation circuit 92 of thesignal processing system of the normal-phase voltage side; thereverse-phase voltages that are divided are input to the abc-dqtransformation circuit 102 of the signal processing system of thereverse-phase voltage side; and the signal processing is performedindependently.

The separation of the normal-phase components and the reverse-phasecomponents of the system voltage is not limited to that described above;for example, the reverse-phase components of the normal-phase componentsmay be divided for each control system by supplying, as thesynchronization signal to the rotating coordinate transformationcircuit, the phase of the PLL output reversed 180°.

Thus, the abc-dq transformation circuit 92 of the signal processingsystem of the normal-phase voltage side outputs the detected values ofthe normal-phase components of the phase voltages. The detected valuesare output as a d-axis component V_(Dn) and a q-axis component V_(Qn).The d-axis component V_(Dn) and the q-axis component V_(Qn) aremutually-orthogonal vectors. The d-axis component V_(Dn) of thenormal-phase voltage is a voltage signal having the same phase as thephase of the normal-phase voltage of the power system, and the q-axiscomponent V_(Qn) is a voltage signal having a phase leading the phase ofthe normal-phase voltage of the power system by 90°.

Similarly, the abc-dq transformation circuit 102 of the signalprocessing system of the reverse-phase voltage side outputs the detectedvalues of the reverse-phase components of the phase voltages. For thesedetected values as well, the two components of a d-axis component V_(Dr)and a q-axis component V_(Qr) that are mutually-orthogonal are output.The d-axis component V_(Dr) of the reverse-phase voltage is a voltagesignal having the same phase as the phase of the reverse-phase voltageof the power system, and the q-axis component V_(Qr) is a voltage signalhaving a phase leading the phase of the reverse-phase voltage of thepower system by 90°.

The low-pass filter 93 is connected to the side of the abc-dqtransformation circuit 92 outputting the d-axis component V_(Dn).Hereinbelow, the low-pass filter is called the LPF and is notated as LPFin the drawings. The LPF 94 is connected to the side of the abc-dqtransformation circuit 92 outputting the q-axis component V_(Qn).

The LPF 103 is connected to the side of the abc-dq transformationcircuit 102 outputting the d-axis component V_(Dr). The LPF 104 isconnected to the side of the abc-dq transformation circuit 102outputting the q-axis component V_(Qr).

When the dq transformation of the normal-phase component of the systemvoltage is performed, a reverse-phase component that has a frequency of2 times the system voltage is superimposed onto a direct-currentnormal-phase component for each of the d-axis component V_(Dn) and theq-axis component V_(Qn). When the dq transformation of the reverse-phasevoltage of the system voltage is performed, a normal-phase voltage thathas a frequency of 2 times the system voltage is superimposed onto adirect-current reverse-phase component for each of the d-axis componentV_(Dr) and the q-axis component V_(Qr).

The direct current components are extracted from the outputs of theabc-dq transformation circuits 92 and 102 by removing the frequencycomponents of 2 times the system voltage by using the LPFs 93, 94, 103,and 104. The extracted direct current components can be usedrespectively as the dq transformation values of the normal-phasevoltages and the reverse-phase voltages.

A d-axis component V_(Dne) of the normal-phase voltages that isextracted is input to the compensation voltage arithmetic part 95 with apreset target value V_(Dn*) for the d-axis of the normal-phase voltagesof the system voltage. In the compensation voltage arithmetic part 95 asdescribed above, a compensation amount that corresponds to thecompensation voltage corresponding to the difference between thenormal-phase d-axis component and the normal-phase d-axis target valueis supplied to the dq-abc transformation circuit 97.

A q-axis component V_(Qne) of the normal-phase voltages that isextracted is input to the PLL 112. As described below relating to thePLL 112, the normal-phase q-axis component is controlled by the PLL 112to be 0. The difference between the normal-phase q-axis componentV_(Qne) and the system normal-phase voltage q-axis target value may becalculated by an adder-subtracter, and the calculated difference may beinput to the dq-abc transformation circuit 97.

The difference between a d-axis component V_(Dre) of the reverse-phasevoltages that is extracted and a target value V_(Dr*) for the d-axis ofthe reverse-phase voltages of the system voltage is calculated by anadder-subtracter (a second arithmetic part) 105, and the difference isinput to the dq-abc transformation circuit 107. The difference between aq-axis component V_(Qre) of the reverse-phase voltages that is extractedand a target value V_(Qr*) for the q-axis of the reverse-phase voltagesof the system voltage is calculated by an adder-subtracter (a secondarithmetic part) 106, and the difference is input to the dq-abctransformation circuit 107.

These outputs and differences correspond to the compensation voltagesfor the phase voltages of the power system and are called thecompensation amounts. The dq-abc transformation circuits 97 and 107receive the inputs of the compensation amounts of the d-axis and thecompensation amounts of the q-axis, perform reverse dq transformationsusing Formula (2), generate compensation amounts including thenormal-phase components and the reverse-phase components of the phasevoltages, and output the compensation amounts.

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack & \; \\{{\begin{bmatrix}a \\b \\c\end{bmatrix}\begin{bmatrix}{\sin\;\omega\; t} & {\cos\;\omega\; t} \\{\sin\left( {{\omega\; t} - {\frac{2}{3}\pi}} \right)} & {\cos\left( {{\omega\; t} - {\frac{2}{3}\pi}} \right)} \\{\sin\left( {{\omega\; t} + {\frac{2}{3}\pi}} \right)} & {\cos\left( {{\omega\; t} + {\frac{2}{3}\pi}} \right)}\end{bmatrix}}\begin{bmatrix}d \\q\end{bmatrix}} & (2)\end{matrix}$

Outputs U_(N), V_(N), and W_(N) of the dq-abc transformation circuit 97of the signal processing system of the normal-phase voltage side areadded respectively to outputs U_(R), V_(R), and W_(R) of the dq-abctransformation circuit 107 of the signal processing system of thereverse-phase voltage side by adders 108 to 110. The output signals thatcorrespond to these compensation amounts are supplied to the gate drivesignal generation circuit 111, are input to the gate drive signalgeneration circuit, and are converted into a gate drive signal tocorrespond to the necessary compensation voltages.

The PLL 112 receives the input of the normal-phase q-axis componentV_(Qne) and generates and outputs a synchronization signal θ to causethe normal-phase q-axis component V_(Qne) that is input to be zero. Theoutput of the PLL 112 is supplied to the abc-dq transformation circuits92 and 102 and the dq-abc transformation circuits 97 and 107. That is,the abc-dq transformation circuits 92 and 102 and the dq-abctransformation circuits 97 and 107 are caused to operate synchronouslywith the phase (the power angle) of the normal-phase voltage of thepower system by the PLL 112.

Generally, in a power system, the three-phase alternating currentvoltages are made of the sum of the zero-phase voltages, thenormal-phase voltages, and the reverse-phase voltages. In the case of athree-phase three-line technique, the zero-phase voltages are zeroconstantly; therefore, it is unnecessary to consider the zero-phasevoltages, and the sum total of the phase voltages of the three phasesalways is zero. Unbalanced voltages are made of the two components ofthe balanced normal-phase voltages and the balanced reverse-phasevoltages. Accordingly, as described above, by dividing the three-phasealternating current into the normal-phase components and thereverse-phase components, processing for generating compensation amountsof the normal-phase components and the reverse-phase components can beperformed. Then, by adding the normal-phase components and thereverse-phase components of the compensation amounts, a pattern of thegate drive signal corresponding to the compensation voltagescorresponding to the phase voltages can be generated easily.

FIG. 3A is a block diagram illustrating a portion of the voltagecompensation device of the embodiment.

A configuration example of the compensation voltage arithmetic part 95of FIG. 2 is schematically shown in FIG. 3A.

As shown in FIG. 3A, the compensation voltage arithmetic part 95includes a calculator 96 a that calculates the system voltage, and asetter 96 b in which the compensation voltage characteristic is set. Theoutput of the LPF 93 is connected to the calculator 96 a, and the d-axiscomponent V_(Dne) of the normal-phase voltages of the system voltage isinput to the calculator 96 a. The preset d-axis target value V_(Dn*) ofthe system normal-phase voltage is input to the calculator 96 a. Thecalculator 96 a calculates a system voltage V_(s) and a target voltageV_(s*) as effective values by multiplying the d-axis component V_(Dne)and the d-axis target value V_(Dn*) by a prescribed constant.

The d-axis component V_(Dne) is equal to the peak value of the phasevoltages of the power system. Also, the d-axis target value V_(Dn*) isset as the peak value of the phase voltages of the power system. In theexample, the effective value of the phase voltage is calculated bydividing each of the d-axis component V_(Dne) and the d-axis targetvalue V_(Dn*) that are input by the square root of 2. Then, bymultiplying the calculated values by the square root of 3, the d-axiscomponent V_(Dne) and the d-axis target value V_(Dn*) each are convertedinto values corresponding to the effective value of the line voltage ofthe power system.

The system voltage V_(s) that is calculated by the calculator 96 a isinput to the setter 96 b, and the target voltage V_(s*) of the systemvoltage is set in the setter 96 b. The setter 96 b outputs acompensation voltage V_(c) corresponding to the system voltage that isinput. Although not illustrated, the value of the compensation voltageV_(c) output from the setter 96 b is converted into a compensationamount corresponding to the compensation voltage by being supplied to adq-abc transformation circuit to match the subsequent processing system.

Here, a specific example of the compensation voltage characteristic ofthe embodiment will be described.

FIG. 3B is a graph showing a setting example of the setter.

As shown in FIG. 3B, the setter 96 b includes data of the compensationvoltage V_(c) for the system voltage V_(s). For example, the firstcontrol circuit 81 stores such data as a table in memory (notillustrated). Or, the data may be generated automatically by setting anunbalanced voltage compensation priority range described below.

In the example, the target voltage V_(s*) of the system voltage V_(s) isset to 6600 V. The characteristic of the setter 96 b is such that whenthe system voltage V_(s) is within the range of 6600 V±100 V, thecompensation voltage V_(c) is 0 V regardless of the magnitude of thesystem voltage V_(s). When the range of the system voltage V_(s) isgreater or less than the range of 6600 V±100 V, different compensationvoltages V_(c) are set according to the system voltage V_(s).

For example, when the system voltage V_(s) is 6900 V (6600 V+300 V), thecompensation voltage V_(c) is set to −300 V; when the system voltageV_(s) is 6300 V (6600 V−300 V), the compensation voltage V_(c) is set to+300 V. That is, the compensation voltage V_(c) is set to be equal tothe difference between the system voltage and the target voltage.

Hereinbelow, a range such as the range of 6600 V±100 V of FIG. 3B inwhich the compensation voltage V_(c) is set to 0 V regardless of thesystem voltage V_(s) is called the unbalanced voltage compensationpriority range. Also, an input voltage range of the system voltage V_(s)such as the range of 6600 V±300 V of FIG. 3B is called the systemvoltage input range, and the range in which the unbalanced voltagecompensation priority range is excluded from the input range of thesystem voltage is called the normal-phase voltage compensation range.

In the embodiment, the relationship between the system voltage and thecompensation voltage of the setter 96 b is set to be different betweenthe unbalanced voltage compensation priority range and the normal-phasevoltage compensation range.

In the unbalanced voltage compensation priority range, the compensationvoltage that corresponds to the reverse-phase voltage can be givenpriority over the normal-phase voltage in the output of the voltagecompensation device 1. By outputting the compensation voltagecorresponding to the reverse-phase component with priority, theunbalanced state of the system voltage can be compensated with priority.

In the normal-phase voltage compensation range, the voltage compensationdevice 1 outputs a compensation voltage to compensate the increaseamount when the system voltage increases, and outputs a compensationvoltage to compensate the decrease amount when the system voltagedecreases. Accordingly, the voltage compensation device 1 performs acompensation operation for the normal-phase voltage with priority.

The voltage value of the specific example described above can be setappropriately and arbitrarily according to the application of thevoltage compensation device 1, etc. Also, the relationship between thesystem voltage and the compensation voltage is not limited to the caseof the example described above. For example, rather than 0 V, thesetting value of the compensation voltage may be set to a constant valuethat is sufficiently small compared to the compensation voltagecorresponding to the system voltage. Also, this is not limited to aconstant value; the compensation voltage may be set to change accordingto the system voltage.

In the output of the voltage compensation device 1 of the embodiment,priority can be given to one of the compensation amount corresponding tothe normal-phase components or the compensation amount corresponding tothe reverse-phase components according to the setting of the unbalancedvoltage compensation range. The compensation voltage that can be outputby the voltage compensation device 1 is limited by the maximum value ofthe output voltage of the first power converter 20; therefore, accordingto the embodiment, the limited output range of the compensation voltagecan be utilized effectively.

The second control circuit 82 (FIG. 2) includes, for example, analternating current control circuit and the like 120. In the example,the alternating current control circuit and the like 120 receives theinput of the current data IL1 and IL2 which is the data of thealternating current supplied via the inductors 51 and 52, receives theinput of the direct current voltage data VDC acquired by the directcurrent voltage detector 75, and controls the active power and thedirect current voltage supplied to the first power converter 20.

Operations of the voltage compensation device 1 of the embodiment willnow be described.

Based on the phase voltages of the upstream side of the power system,the voltage compensation device 1 of the embodiment compensates thevoltage for each phase so that each voltage becomes the prescribed phasevoltage. When the phase voltages of the downstream side are less thanthe prescribed value, compensation voltages are added so that the phasevoltages of the downstream side become the prescribed value. When thephase voltages of the downstream side are not less than the prescribedvalue, compensation voltages are subtracted so that the phase voltagesof the downstream side become the prescribed value.

The compensation of the phase voltages is performed by setting thevoltages and the phases generated at the secondary windings 11 s, 13 s,and 15 s. For example, when the prescribed value of the phase voltage ofthe U-phase is X [V] and the actual phase voltage of the U-phase is X[V]−Δx [V], the voltage compensation device 1 outputs dx [V] having thesame phase as the power system to the secondary winding 11 s. The phasevoltage of the downstream side is set to X [V] by the series transformer11. When the actual phase voltage of the U-phase is X [V]+Δx [V], thevoltage compensation device 1 outputs, to the secondary winding 11 s, Δx[V] having a phase 180° different from that of the power system. Thephase voltage of the downstream side is set to X [V] by the seriestransformer 11.

The compensation operations described above are performed independentlyfor the normal-phase voltages and the reverse-phase voltages of thepower system according to the generated compensation amounts. Thecompensation amounts that are generated by the control system of thenormal-phase voltage side are generated with priority when thenormal-phase components of the system voltage are greater or less thanthe unbalanced compensation priority range. The compensation amountsthat are generated by the control system of the reverse-phase voltageside are generated with priority when the normal-phase voltages arewithin the unbalanced compensation priority range.

That is, the voltage compensation device 1 of the embodiment compensatesthe voltage values by adding the compensation voltages, etc., when thevoltage values of the system voltage are greater or less than the targetvoltages. Even when the fluctuations of the voltage values of the systemvoltage are small, if there are unbalanced voltages, the unbalancedstate is compensated by outputting the compensation voltages based onthe compensation amounts generated by the reverse-phase voltage side.

In the voltage compensation device 1 of the embodiment, the phasevoltage of each phase can be compensated because the dq transformationsare performed by dividing the normal-phase components and thereverse-phase components. Therefore, in addition to the voltagecompensation of the balanced voltages, voltage compensation can beperformed also for the unbalanced state occurring at the upstream side,and balanced voltages can be supplied downstream.

Even when the range of the normal-phase voltage is within the unbalancedvoltage compensation priority range, the first control circuit 81 cangenerate the compensation amount based on a q-axis target value V_(Qn*)and perform a compensation operation according to the compensationamount. That is, when the range of the normal-phase voltage is withinthe unbalanced voltage compensation priority range, the voltagecompensation device 1 can operate as a reactive power compensationdevice and supply reactive power to the power system.

Effects of the voltage compensation device 1 of the embodiment will nowbe described while comparing to a voltage compensation device 200 of acomparative example.

FIG. 4 is a block diagram illustrating the voltage compensation deviceof the comparative example.

As shown in FIG. 4, the voltage compensation device 200 of thecomparative example includes series transformers 211, 213, and 215, tapchanger circuits 220 a and 220 b, parallel transformers 241 and 242,alternating current voltage detectors 271 to 274, and a controller 280.In the voltage compensation device 200 of the comparative example, theprimary windings of the series transformers 211, 213, and 215 areconnected in series to the phases of the power system. One end of eachof the secondary windings of the series transformers 211, 213, and 215are connected to each other. The other end of the secondary winding ofthe series transformer 211 is connected to one terminal of the tapchanger circuit 220 a. The other end of the secondary winding of theseries transformer 213 is connected to the other terminal of the tapchanger circuit 220 a. The other end of the secondary winding of theseries transformer 213 also is connected to one terminal of the tapchanger circuit 220 b. The other end of the secondary winding of theseries transformer 215 is connected to the other terminal of the tapchanger circuit 220 b.

The tap changer circuit 220 a includes switch circuits 222 a to 222 fcorresponding to the number of taps on the secondary side of theparallel transformer 241. In the switch circuits 222 a to 222 f,bidirectional switch circuits in which thyristors are connected inanti-parallel are connected in series, and the number of bidirectionalswitch circuits connected in series is equal to the number of taps onthe secondary side of the parallel transformer 241. The tap changercircuit 220 b has the same circuit configuration as the tap changercircuit 220 a. In switch circuits 222 g to 222 m, bidirectional switchcircuits in which thyristors are connected in anti-parallel areconnected in series, and the number of bidirectional switch circuitsconnected in series is equal to the number of taps on the secondary sideof the parallel transformer 242.

The primary winding of the parallel transformer 241 is connected betweendownstream (the u-phase) of the U-phase and downstream (the v-phase) ofthe V-phase. The primary winding of the parallel transformer 242 isconnected between downstream (the v-phase) of the V-phase and downstream(the w-phase) of the W-phase. Each of the taps of the secondary windingsof the parallel transformers 241 and 242 is connected to a seriesconnection node of the bidirectional switches.

The alternating current voltage detectors 271 to 274 are connectedsimilarly to the alternating current voltage detectors 71 to 74 of thevoltage compensation device 1 of the embodiment.

The controller 280 includes an upper limit and a lower limit of a targetvoltage of the voltage of the power system. Signals Vtg1 and Vtg2 thattrigger the gates of the thyristors are generated by comparing thedetection results of the alternating current voltage detectors 271 to274 and the upper limit and the lower limit of the target voltage.

Contactors 291 and 292 are connected to two ends for the tap changercircuits 220 a and 220 b. The contactors 291 and 292 operate when thethyristors of the tap changer circuits 220 a and 220 b are turned OFFforcibly.

In the voltage compensation device 200 of the comparative example, thesecondary windings of the series transformers 211, 213, and 215 and thesecondary windings of the parallel transformers 241 and 242 areconnected by the bidirectional switches 222 a to 222 m using thyristors.The controller 280 compares the detection results of the alternatingcurrent voltage detectors 271 to 274 and the preset upper limit andlower limit of the target voltage. Then, for each of the phases, whenthe voltage is less than the lower limit of the target value, thecontroller 280 controls the bidirectional switches to connect to tapsoutputting a higher voltage to increase the voltage of the primarywinding of the series transformer. For example, when the downstreamvoltage of the U-phase is low, the controller 280 generates the gatedrive signal to switch the bidirectional switches 222 c and 222 d ON.The bidirectional switches 222 c and 220 d are connected to the taps ofthe parallel transformer 241 generating the highest voltage. When thedownstream voltage of the U-phase is high, the controller 280 generatesthe gate drive signal to switch the bidirectional switches 222 a and 222f ON. The bidirectional switches 222 a and 222 f are connected to thetaps of the parallel transformer 241 generating the highest voltage, andthe voltage of the connected taps is applied with the reverse phase ofthe voltage of the U-phase.

Thus, in the voltage compensation device 200 of the comparative example,the voltages of the series transformers 211, 213, and 215 arecompensated by switching between the taps provided in the paralleltransformers 241 and 242; therefore, the setting value of thecompensation voltage has discrete values dependent on the number oftaps. In the voltage compensation device 200 of the comparative example,the compensation voltage is discrete; therefore, additional equipmentsuch as a reactive power compensation device, etc., are necessaryfurther downstream of the power system, the system is complex, and thecost also increases.

Also, in the voltage compensation device 200 of the comparative example,the compensation voltage can only be set discretely; therefore, it isdifficult to compensate unbalanced voltages by setting the voltage foreach phase. Accordingly, when an unbalanced load is connected todownstream in the power system, etc., there is a risk that effects ofthe unbalanced load also may occur upstream in the power system.

Also, in the bidirectional switches using the thyristors in the voltagecompensation device 200 of the comparative example, a time for ½ of theperiod of the voltage of each phase of the power system is necessarywhen switching between the taps of the parallel transformers 241 and242. Therefore, the response time of the voltage compensation device 200is constrained by the period of the power system.

Compared to such a voltage compensation device 200 of the comparativeexample, in the voltage compensation device 1 of the embodiment, thedetected voltage data and the compensation amounts for the first powerconverter 20 are generated as substantially continuous data in the firstcontrol circuit 81. For example, the values of the alternating currentvoltage data VAC1 and VAC2 are read by analog/digital converters (ADconverters); therefore, the precision of these data is increased to thelevel determined by the resolution of the AD converters. Accordingly,compensation voltages that have substantially continuous values can beset. In the power system using the voltage compensation device 1 of theembodiment, a device or a system for increasing the precision of thecompensation voltages is unnecessary; therefore, the entire system canbe simple for the system, and the cost can be reduced.

Also, in the voltage compensation device 1 of the embodiment asdescribed above, the compensation voltages can be set independently foreach of the normal-phase voltages and the reverse-phase voltages of thepower system; therefore, the compensation of unbalanced voltages alsocan be performed. Also, the priority of the compensation amountscorresponding to the normal-phase voltages and the compensation amountscorresponding to the reverse-phase voltages of the power system can beset appropriately by the compensation voltage arithmetic part 95.Therefore, the voltage compensation and the unbalanced compensation canbe performed by effectively utilizing the maximum voltage that can beoutput by the first power converter 20.

Also, in the voltage compensation device 1 of the embodiment, thevoltage compensation is performed by power converters using selfarc-extinguishing type switching elements; therefore, the voltagecompensation operation can be performed quickly regardless of the periodof the power system.

Conventionally, contrivances for compensating the voltage has beenperformed at locations where it is predicted that the voltage of thepower system may decrease according to the distance from the powersubstation, etc. For example, at the system end where the voltage dropof a pole transformer is predicted, the tap positions are preset to ahigh voltage, etc. Also, for the system impedance, phase-advancingcapacitors that support the voltage by supplying leading reactive poweralso are used. However, these countermeasures are countermeasurespresupposing that the consumers consume electrical power; when theelectrical power demand decreases such as at night, a problem occurs inthat the system voltage is increased unnecessarily.

To cope with such problems, a TVR (Thyristor Voltage Regulator) such asthe voltage compensation device 200 of the comparative example has beenproposed. As described above, the TVR has the function of varying thecompensation voltage according to the system voltage; therefore, theelectrical power drop in the daytime when the electrical power demand islarge can be accommodated, and the voltage increase at night also can beaccommodated.

However, the TVR performs the voltage compensation operation bycontrolling the voltages applied to the series transformers by switchingbetween the parallel transformer taps by using thyristors; therefore,the response time is slow; the compensation voltages in the voltagecompensation operation are discontinuous due to being dependent on thetransformer taps; and conditions such that voltage abnormalities cannotbe compensated are occurring in recent power systems in which thereverse power flow is increasing as domestic solar power generationbecomes widespread.

In the voltage compensation device 1 of the embodiment, not onlycontinuous voltage compensation but also independent voltagecompensation of the phases is possible; thereby, the voltagecompensation of the power systems of higher complexity of recent yearscan be performed quickly and effectively.

Modification of First Embodiment

FIG. 5 is a block diagram illustrating a voltage compensation device 1 aof the modification. The secondary windings 11 s, 13 s, and 15 s of theseries transformers 11, 13, and 15 has a star connection. The secondarywindings 11 s, 13 s, and 15 s are not limited to a star connection, andcan have a delta connection.

Other than the electrical connection of the secondary windings 11 s, 13s, and 15 s of the series transformers 11, 13, and 15, the voltagecompensation device 1 a of the modification is the same as the voltagecompensation device 1 of the first embodiment; the same components aremarked with the same reference numerals; and a detailed description isomitted.

In the voltage compensation device 1 a of the modification as shown inFIG. 5, the secondary winding 11 s of the series transformer 11 of avoltage compensator 10 a includes the terminals 12 a and 12 b. Thesecondary winding 13 s of the series transformer 13 includes theterminals 14 a and 14 b. The secondary winding 15 s of the seriestransformer 15 includes the terminals 16 a and 16 b. The one-terminals12 a, 14 a, and 16 a are winding start positions of the secondarywindings 11 s, 13 s, and 15 s, and the other-terminals 12 b, 14 b, and16 b are the winding end positions. The one terminal 12 a is connectedto the other terminal 14 b, the one terminal 14 a is connected to theother terminal 16 b, and the one terminal 16 a is connected to the otherterminal 12 b. The connection node of the terminals 12 a and 14 b isconnected to the alternating current output terminal 22 b of the firstpower converter 20. The connection node of the terminals 14 a and 16 bis connected to the alternating current output terminal 22 c of thefirst power converter 20. The connection node of the terminals 16 a and12 b is connected to the alternating current output terminal 22 a of thefirst power converter 20. That is, the secondary windings 11 s, 13 s,and 15 s of the series transformers 11, 13, and 15 have a deltaconnection and are connected to the alternating current output terminals22 a, 22 b, and 22 c of the first power converter 20.

The voltage compensation device 1 a of the modification operatessimilarly to the voltage compensation device 1 of the first embodiment.Namely, when the voltage across the series transformer is less than thelower limit of the target voltage, a voltage that corresponds to theinsufficient voltage amount of the same phase as the primary winding isgenerated in the secondary winding and added to the voltage of theprimary winding via magnetic coupling. When the voltage across theseries transformer is greater than the upper limit of the targetvoltage, a voltage that corresponds to the insufficient voltage amountof the reverse phase of the primary winding is generated in thesecondary winding and added to, i.e., subtracted from, the primarywinding via magnetic coupling.

Actions and effects of the voltage compensation device 1 a of theembodiment will now be described.

When series transformers that have a star connection are connected tothe output of the first power converter 20, an advantage is provided inthat the electrical connection operation is easy because theone-terminals of the secondary windings are connected to the output ofthe first power converter 20. On the other hand, in a star connection,the other-terminals of the secondary windings are connected to eachother as a neutral point, but the neutral point is not connectedelsewhere; the current cannot flow elsewhere when voltage distortionoccurs due to nonlinearity of the transformers, etc.; therefore, thereare cases where problems occur in that the voltage distortion phenomenonis not resolved easily.

When the series transformers having a delta connection are connected tothe output of the first power converter 20, the electrical connectionoperation is complex because the secondary windings of the phases areconnected to each other, etc.; on the other hand, a return current canbe caused to flow through the secondary windings. Therefore, in thevoltage compensation device 1 a, voltage distortion does not occureasily, and high-quality electrical power can be connected to the powersystem.

In the voltage compensation device 1 a of the embodiment, the secondarywindings 11 s, 13 s, and 15 s of the series transformers 11, 13, and 15that are connected to the output of the first power converter 20 have adelta connection; therefore, a connection of high-quality electricalpower having low voltage distortion is possible.

One of a star connection or a delta connection is applicable to thesecondary windings 11 s, 13 s, and 15 s of the series transformers 11,13, and 15 also in the other embodiments described below.

Second Embodiment

FIG. 6 is a block diagram illustrating a portion of a voltagecompensation device of the embodiment.

An example of the elements of a compensation voltage arithmetic part 195of the case of the embodiment is schematically shown in FIG. 6.

As shown in FIG. 6, the compensation voltage arithmetic part 195includes a calculator 196 a that calculates the system voltage, and thesetter 96 b in which a compensation voltage characteristic is set. Inthe embodiment, the configuration of the calculator 196 a is differentfrom those of the other embodiments described above, and the otherelements are the same as those of the other embodiments described above.

The calculator 196 a receives the input of the d-axis component V_(Dne)of the normal-phase voltages of the system and the d-axis target valueV_(Dn*) of the normal-phase voltages of the system and receives theinput of the alternating current voltage data VAC1 and VAC2 suppliedfrom the alternating current voltage detectors 71 and 72. Based on theseinputs, the calculator 196 a calculates the effective values of thesystem voltage V_(s) and the target value V_(s*) of the system voltageV_(s) and supplies the effective values to the setter 96 b.

More specifically, the calculator 196 a calculates the effective valuesof the phases by calculating the mean square values of the alternatingcurrent voltage data VAC1 and VAC2 which are the line voltages of thethree-phase alternating current. The calculator 196 a averages theeffective values of the phases that are calculated and uses the averageas the effective value of the system voltage.

In the setter 96 b, the compensation voltage V_(c) for the systemvoltage V_(s) calculated by the calculator 196 a is designated, and thetarget voltage V_(s*) of the system voltage V_(s) is set.

Thus, the target value and/or the measured value of the system voltagecan be obtained appropriately from the value of the normal-phase d-axiscomponent.

Third Embodiment

FIG. 7 is a block diagram illustrating a portion of a voltagecompensation device of the embodiment.

A portion of a first control circuit 81 b is shown in FIG. 7. The partsbeyond the outputs of the dq-abc transformation circuits 97 and 107 thatare not shown in the drawing are the same as those of the firstembodiment described above, etc.

In the other embodiments described above, the case is described wherethe unbalanced voltage compensation is performed by a compensationcorresponding to the reverse-phase voltages without substantiallyperforming a compensation corresponding to the normal-phase voltageswhen the range is within the unbalanced voltage compensation priorityrange. More specifically, the case is described in the embodiment wherea voltage compensation that has higher precision is performed byassigning a priority order to the compensation corresponding to thenormal-phase voltages and the compensation corresponding to thereverse-phase voltages. Because there is an upper limit to the voltagethat can be output by the first power converter 20 as described above,for example, in the normal-phase voltage compensation range, a priorityorder is assigned to the d-axis component and the q-axis component, anda priority order is assigned between the normal-phase voltagecompensation and the reverse-phase voltage compensation.

In the embodiment as shown in FIG. 7, the first control circuit 81 bfurther includes limiters 131, 133, 135, 136, 138, and 140, arithmeticcircuits 132, 134, 137, and 139, a comparator 141, and switches 142 aand 142 b.

The limiter 131 is provided between the compensation voltage arithmeticpart 95 and the dq-abc transformation circuit 97. The limiter (a firstlimiter) 131 limits the input signal to be within the range of±V_(comp_max). When the amplitude of the signal input to the limiter 131is within ±V_(comp_max) range, the input signal is output as-is. Whenthe amplitude of the signal input to the limiter 131 is outside±V_(comp_max), the limiter 131 outputs ±V_(comp_max). The signal that isoutput from the limiter 131 is input to the dq-abc transformationcircuit 97 as a compensation amount V_(comp_Dn_ref) of the normal-phased-axis component.

Positive and negative limit values are provided in each of the limiters.In the drawing as well, although not illustrated to avoid complexity,limit values on the negative side also are provided. Unless otherwisespecified hereinbelow, when referring to the limit value of the limiter,the limit value on the negative side also is provided, and the absolutevalues of the positive and negative limit values are equal. When theinput signal is within the range of the positive and negative limitvalues, the input signal is output as-is; when the input signal isoutside the positive or negative limit value, the input signal islimited to the limit value. However, the limit values are not limited tothe case of positive and negative values having equal absolute values,and any setting may be used.

The target value of the normal-phase q-axis is input to the input of thelimiter (a second limiter) 133. The output of the limiter 133 isconnected to the dq-abc transformation circuit 97. The limit value ofthe limiter 133 is set to a limit value V_(comp_Qn_max) of thenormal-phase q-axis component compensation amount. Although elaboratedbelow, the limit value V_(comp_Qn_max) changes according to a maximumcompensation amount V_(comp_max) and the compensation amountV_(comp_Dn_ref). The value of the limit value V_(comp_Qn_max) is set bybeing calculated by the arithmetic circuit 132. The maximum compensationamount V_(comp_max) is preset based on the maximum voltage of the firstpower converter 20.

The limiter (a third limiter) 135 is provided between theadder-subtracter 105 and the dq-abc transformation circuit 107 of thesignal processing system of the reverse-phase voltage side. The limitvalue of the limiter 135 is set to a limit value V_(comp_DQr_max) of thereverse phase compensation amount. Although elaborated below, the limitvalue V_(comp_DQr_max) changes according to the maximum compensationamount V_(comp_max), the compensation amount V_(comp_Dn_ref), and acompensation amount V_(comp_Qn_ref) of the normal-phase q-axiscomponent. The value of the limit value V_(comp_DQr_max) is set by beingcalculated by the arithmetic circuit 134.

The limiter (a fourth limiter) 136 is provided between theadder-subtracter 106 and the dq-abc transformation circuit 107 of thesignal processing system of the reverse-phase voltage side. The limitvalue of the limiter 136 is set to the limit value V_(comp_DQr_max).

The limiter 138 is provided between the adder-subtracter 106 and thedq-abc transformation circuit 107. The limit value of the limiter 138 isset to a limit value V_(comp_DQr_max) of the reverse-phase q-axiscompensation amount. Although elaborated below, the limit valueV_(comp_DQr_max) changes according to the limit value V_(comp_DQr_max)and a compensation amount V_(comp_Dr_ref) of the reverse-phase d-axiscomponent. The value of the limit value V_(comp_Qr_max) is set by beingcalculated by the arithmetic circuit 137.

The limiter 140 is provided between the adder-subtracter 105 and thedq-abc transformation circuit 107. The limit value of the limiter 140 isset to a limit value V_(comp_Dr_max) of the reverse-phase d-axiscompensation amount. As elaborated below, the limit valueV_(comp_Dr_max) changes according to the limit value V_(comp_DQr_max)and a compensation amount V_(comp_Qr_ref). The value of the limit valueV_(comp_Dr_max) is set by being calculated by the arithmetic circuit139.

The comparator 141 compares the size relationship of the magnitudes ofthe outputs of the adder-subtracters 105 and 106. That is, thecomparator 141 compares the magnitudes of an output value V_(comp_Dr) ofthe reverse-phase d-axis output from the adder-subtracter 105 and anoutput value V_(comp_Qr) of the reverse-phase q-axis output from theadder-subtracter 106. For example, the comparator 141 outputs thelogical value of 1 when V_(comp_Dr)≥V_(comp_Qr). The logical value of 0is output when V_(comp_Dr)<V_(comp_Qr).

The switch 142 a is connected between the dq-abc transformation circuit107 and the limiters 135 and 140. The switch 142 a connects the outputof the limiter 135 or the output of the limiter 140 to the dq-abctransformation circuit 107 by switching. The connection destination ofthe switch 142 a is switched according to the input of the logicalvalue; for example, in the case of the logical value of 1, the output ofthe limiter 135 is selected, and the output of the limiter 135 issupplied to the dq-abc transformation circuit 107. When the logicalvalue of 0 is input, the switch 142 a selects the output of the limiter140, and the output of the limiter 136 is supplied to the dq-abctransformation circuit 107.

The switch 142 b is connected between the dq-abc transformation circuit107 and the limiters 138 and 136. The switch 142 b inputs the output ofthe limiter 138 or the output of the limiter 136 to the dq-abctransformation circuit 107 by switching. The connection destination ofthe switch 142 b is switched according to the input of the logicalvalue; for example, in the case of the logical value of 1, the output ofthe limiter 138 is selected, and the output of the limiter 138 issupplied to the dq-abc transformation circuit 107. When the logicalvalue of 0 is input, the switch 142 b selects the output of the limiter136, and the output of the limiter 136 is supplied to the dq-abctransformation circuit 107.

That is, when V_(comp_Dr)≥V_(comp_Qr), the compensation amountV_(comp_Dr_ref) that is output from the limiter 135 and the compensationamount V_(comp_Qr_ref) that is output from the limiter 138 each areinput to the dq-abc transformation circuit 107. WhenV_(comp_Dr)<V_(comp_Qr), the compensation amount V_(comp_Dr_ref) that isoutput from the limiter 140 and the compensation amount V_(comp_Qr_ref)that is output from the limiter 136 each are input to the dq-abctransformation circuit 107.

Operations of the voltage compensation device of the embodiment will nowbe described.

FIG. 8A and FIG. 8B are conceptual views for describing the operationsof the voltage compensation device of the embodiment.

In the voltage compensation device of the embodiment, the compensationamount that is generated according to an output other than thenormal-phase d-axis component is used with priority when the magnitudeof the normal-phase d-axis component is within the unbalanced voltagecompensation range. In such a case, the compensation amount that isgenerated according to the magnitude of the normal-phase q-axiscomponent (=the magnitude of the normal-phase q-axis target value) isgiven priority; therefore, the voltage compensation device functions asa reactive power compensation device.

Also, in the voltage compensation device of the embodiment, when themagnitude of the normal-phase d-axis component is within thenormal-phase voltage compensation range, the compensation amount isgenerated with priority in the order of the normal-phase d-axiscomponent, the normal-phase q-axis component, and the magnitude of thereverse-phase voltage. In the signal processing system of thereverse-phase voltage side, the compensation amount is allotted withpriority to the greater of the magnitude of the reverse-phase d-axiscomponent or the magnitude of the reverse-phase q-axis component.

As shown in FIG. 8A, the normal-phase components of the compensationamount are illustrated by vectors on a two-dimensional plane having thed-axis and the q-axis. The d-axis and the q-axis are orthogonal. Theradius of a circle Cn illustrates the maximum compensation amountV_(comp_max). That is, the radius of the circle Cn is the maximumcompensation amount V_(comp_max) corresponding to the maximum voltage ofthe first power converter 20. The vector that is parallel to the d-axisillustrates the compensation amount V_(comp_Dn_ref). The vector that isparallel to the q-axis illustrates the compensation amountV_(comp_Qn_ref).

When allotting the output with priority to the normal-phase componentsof the compensation amount, the maximum compensation amount V_(comp_max)is equal to the compensation amount V_(comp_Dn_ref). This is a vectorsum with the compensation amount V_(comp_Qn_ref). A compensation amountV_(comp_inv) is determined by the following Formula (3) by thePythagorean theorem. Here, V_(comp_Dn) and V_(comp_Qn) respectively arethe outputs of the LPFs 93 and 94 and are called the output value of thenormal-phase d-axis and the output value of the normal-phase q-axis.[Formula 3]V _(comp_inv)=√{square root over (V _(comp_Dn) ² +V _(comp_Qn) ²)}  (3)

In the embodiment, it is possible to output the output value V_(comp_Dn)of the normal-phase d-axis up to a limit value V_(comp_Dn_max) which isits maximum value. V_(comp_Dn_max) at this time is equal to the maximumcompensation amount V_(comp_max). When the compensation amountV_(comp_Dn_ref) is less than V_(comp_max), the excess amount is allottedto the output value V_(comp_Qn). The limit value V_(comp_Qn_max) at thistime is determined by Formula (4) by replacing the compensation amountV_(comp_inv) with the maximum compensation amount V_(comp_max). Thecalculation of Formula (4) is performed by the arithmetic circuit 132.[Formula 4]V _(comp_Qn_max)=√{square root over (V _(comp_max) ² −V _(comp_Dn_ref)²)}  (4)

That is, the compensation amount V_(comp_Qn_max) is set using themaximum compensation amount V_(comp_max) and the compensation amountV_(comp_Dn_ref).

When the compensation amount of the normal-phase d-axis is within theunbalanced voltage compensation range, for example, it is sufficient toset V_(comp_Dn_ref)=0 in Formula (4). Accordingly, the compensationamount of the normal-phase q-axis can be output up to the maximumcompensation amount V_(comp_max).

FIG. 8B shows the case where the magnitudes of the normal-phasecomponents of the compensation amount are less than the maximumcompensation amount V_(comp_max), an excess of the compensation amountoccurs, and the excess amount is allotted to the reverse-phasecomponents. An inner circle Cr of the circle Cn schematicallyillustrates the trajectory of the vectors of the reverse-phasecomponents. The reverse-phase components are vectors that rotate throughthe circle Cr at an angular velocity ω in the reverse direction of thenormal-phase components. The compensation amount of the normal-phasecomponents is the compensation amount V_(comp_inv) of Formula (3). Theallotment to the reverse-phase components is possible due to thedifference between the maximum compensation amount V_(comp_max) and thecompensation amount V_(comp_inv) of the normal-phase components which isdetermined by Formula (5). The calculation of Formula (5) is performedby the arithmetic circuit 134.[Formula 5]V _(comp_DQr_max) =V _(comp_max)−√{square root over (V _(comp_Dn_ref) ²+V _(comp_Qn_ref) ²)}  (5)

The limit value V_(comp_DQr_max) is illustrated by the magnitude of thevector sum of the compensation amount V_(comp_Dr_ref) and thecompensation amount V_(comp_Qr_ref). In the embodiment, which of thecompensation amount V_(comp_Dr_ref) or the compensation amountV_(comp_Qr_ref) is given priority is determined by the size relationshipof the output value V_(comp_Dr) and the output value V_(comp_Qr) beforethe limiter input. The size relationship of V_(comp_Dr) and V_(comp_Qr)is compared by the comparator 141. The connections of the switches 142 aand 142 b are switched according to the output of the comparator 141.

The d-axis output is given priority when V_(comp_Dr)≥V_(comp_Qr).Therefore, the limit value V_(comp_Qr_max) changes according to thecompensation amount V_(comp_Dr_ref). The limit value V_(comp_Qr_max) isdetermined by Formula (6). The calculation of Formula (6) is performedby the arithmetic circuit 137.[Formula 6]V _(comp_Qr_max)=√{square root over (V _(comp_DQr_max) ² −V_(comp_Dr_ref) ²)}  (6)

The q-axis output is given priority when V_(comp_Dr)<V_(comp_Qr).Therefore, the limit value V_(comp_Dr_max) changes according to thecompensation amount V_(comp_Qr_ref). The limit value V_(comp_Dr_max) isdetermined by Formula (6′). The calculation of Formula (6′) is performedby the arithmetic circuit 139.[Formula 7]V _(comp_Dr_max)=√{square root over (V _(comp_DQr_max) ² −V_(comp_Qr_ref) ²)}  (6′)

When the compensation amount of the normal-phase d-axis is within theunbalanced voltage compensation range, for example, it is sufficient toset V_(comp_Dn_ref)=0 in Formula (5). The magnitude of the compensationamount of the reverse-phase voltage part is set according to themagnitude of the compensation amount of the normal-phase q-axis, and themagnitudes of the compensation amounts of the d-axis component and theq-axis component are set according to Formula (6) and Formula (6′).

Effects of the voltage compensation device of the embodiment will now bedescribed.

In the voltage compensation device of the embodiment, the compensationamounts are limited in the first control circuit 81 b so that themaximum voltage of the first power converter 20 is not exceeded. Thelimits of the compensation amounts are set so that the normal-phasecomponents can be output with priority among the normal-phase componentsand the reverse-phase components. Therefore, even when largecompensation amounts are output by the abc-dq transformation circuits 92and 102, the compensation amounts of the reverse-phase components aremore limited and are limited to be not more than the maximumcompensation amount. Therefore, the voltage compensation device canoutput compensation voltages without distortion.

The compensation amounts of the reverse-phase components can be outputwith priority to selecting the greater of the d-axis component and theq-axis component; therefore, the contribution of the one having thegreater effect on the unbalanced voltage can be increased.

In the multiple embodiments described above, the configuration of thecontrol circuit is set based on which among the normal-phase componentsor the reverse-phase components of the compensation amounts to allotwith priority, and which among the d-axis component or the q-axiscomponent of the normal-phase components or the reverse-phase componentsto allot with priority. Whether or not to secure any component withpriority as the compensation amount is not limited to the foregoingdescription and can be set arbitrarily in an appropriate range.

According to the embodiments described above, a voltage compensationdevice can be realized in which the voltage of the power system iscompensated quickly and continuously to an appropriate value.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention. Moreover, above-mentioned embodiments can becombined mutually and can be carried out.

The invention claimed is:
 1. A voltage compensation device, comprising:a power converter including an inverter circuit including a switchingelement, the switching element being of a self arc-extinguishing type;series transformers including primary windings connected in series tophases of a three-phase alternating current, and secondary windingsconnected to an output of the power converter; and a controllergenerating a drive signal based on voltages of the phases of thethree-phase alternating current and supplying the drive signal to thepower converter, the drive signal driving the switching element, thecontroller including a first coordinate transformation circuitgenerating a first output and a second output by performing a rotatingcoordinate transformation of normal-phase components of the three-phasealternating current, the first output being a vector component of a samephase as the normal-phase components, the second output being a vectorcomponent orthogonal to the first output, a first arithmetic partcalculating a system voltage indicating a voltage value of thethree-phase alternating current based on a direct current component ofthe first output, and generating a first compensation amountcorresponding to a compensation voltage set to compensate a shift of thesystem voltage from a preset target voltage, a second coordinatetransformation circuit generating a third output and a fourth output byperforming a rotating coordinate transformation of reverse-phasecomponents of the three-phase alternating current, the third output andthe fourth output being orthogonal to each other, and a secondarithmetic part generating a second compensation amount based on adirect current component of the third output and a direct currentcomponent of the fourth output, the second compensation amount being acompensation amount of a reverse-phase component of the system voltage,the controller generating the drive signal based on the firstcompensation amount and the second compensation amount, the firstarithmetic part generating the first compensation amount correspondingto the compensation voltage when the system voltage is outside aprescribed range, generating the first compensation amount to be lessthan compensation amount corresponding to the compensation voltage whenthe system voltage is within the prescribed range, the controllergenerating the drive signal based on the first compensation amount withhigher priority than the second compensation amount when the systemvoltage is outside the prescribed range, generating the drive signalbased on the second compensation amount with higher priority than thefirst compensation amount when the system voltage is within theprescribed range, the controller including a first limiter limiting anamplitude, the first output being input to the first limiter, a secondlimiter limiting an amplitude, a target value for the second outputbeing input to the second limiter, a third limiter limiting anamplitude, the third output being input to the third limiter, a fourthlimiter limiting an amplitude, the fourth output being input to thefourth limiter, a first filter extracting a direct current componentfrom the first output, a second filter extracting a direct currentcomponent from the second output, a third filter extracting a directcurrent component from the third output, and a fourth filter extractinga direct current component from the fourth output, limit values of thefirst limiter, the second limiter, the third limiter and the fourthlimiter being set to cause a magnitude of a vector sum of an output ofthe first filter, an output of the second filter, an output of the thirdfilter and an output of the fourth filter to be not more than a maximumcompensation amount corresponding to a maximum value output by the powerconverter.
 2. The voltage compensation device according to claim 1,wherein the first arithmetic part generates the first compensationamount to cause the compensation voltage to be 0 when the system voltageis within the prescribed range.
 3. The voltage compensation deviceaccording to claim 1, wherein when a magnitude of a vector sum of thefirst output and the target value is not more than the maximumcompensation amount, the limit value of the second limiter is set basedon magnitudes of the maximum compensation amount and the first output.4. The voltage compensation device according to claim 3, wherein amagnitude of a vector sum of the limit value of the third limiter andthe limit value of the fourth limiter is set based on the maximumcompensation amount, a magnitude of the output of the first limiter, anda magnitude of the output of the second limiter.
 5. The voltagecompensation device according to claim 4, wherein the limit value of thefourth limiter is set based on the magnitude of the output of the thirdfilter when a magnitude of the output of the third filter is not lessthan a magnitude of the output of the fourth filter, and the limit valueof the third limiter is set based on the magnitude of the output of thefourth filter when the output of the fourth filter is greater than theoutput of the third filter.
 6. The voltage compensation device accordingto claim 1, wherein the first arithmetic part calculates the systemvoltage by performing a prescribed calculation on the direct currentcomponent of the first output.
 7. The voltage compensation deviceaccording to claim 1, wherein the first arithmetic part calculates thesystem voltage based on an alternating current voltage between thephases of the three-phase alternating current.